Academic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public defence in Keckmaninsali (HU106), Linnanmaa, on 9 October 2015, at 12 noon

Abstract

Restoration is considered to be a crucial action in order to maintain and enhance ecosystem functioning and halt the decline of biodiversity. Within forested ecosystems, heavily exploited forests have lost a great part of their biodiversity values, and even nature conservation is insufficient to prevent the loss of habitats and the endangerment of species. The aim of this thesis was to provide new information on the impacts of forest restoration methods on boreal forest naturalness, including forest structure, forest-dwelling species and ecosystem processes and functions. This information is needed to develop the restoration methods and their cost-efficiency and to support decision-making concerning restoration and nature conservation. The restoration methods studied were felling with a chainsaw either without or with subsequent burning, and storm treatment, in which the trees were uprooted with an excavator. The variables measured were vegetation assemblages, deadwood dynamics, and deadwood-dependent insect assemblages. In addition to field measurements, a simulation approach was used so as to predict deadwood continuity after different restoration methods. The main finding of this thesis is that the aspects of naturalness studied were most enhanced by burning, whereas felling had the least effect. Restoration burning increased deadwood volume and diversity, enabled the establishment of pioneer plants, increased the relative cover of the forest keystone species Vaccinium myrtillus, enhanced the regeneration of the keystone tree Populus tremula, and provided habitat for red-listed, especially pyrophilous beetles (Coleoptera) and flat bugs (Heteroptera: Aradidae). Felling only increased the volume of deadwood. Storm treatment with tree uprooting was a more effective method than felling with a chainsaw, due to the additional disturbance it caused to ground, enhancing the regeneration of e.g. Pinus sylvestris. According to simulation models, compared to controls restored stands are predicted to have greater deadwood volumes at least for 40 years. The study shows that restoration can be used to accelerate the development of degraded forests towards a higher level of naturalness. The results can be used to choose appropriate restoration methods for forests, based on their initial stage and the goal set for the level of their naturalness.